Systems for generating laser energy are well known in the art and generally include a laser medium, power supply, a pump chamber and an optical cavity or resonator. During operation, the power supply excites the laser medium in the pump chamber which causes light to be generated. The light is concentrated by the resonator to stimulate the emission of laser energy.
The wavelength of the laser energy is determined by the laser medium. For example, a laser medium such as yttrium scandium gallium garnet doped with holmium (Ho:YSGG) provides laser energy having a wavelength of 2.088 .mu.m.
Holmium, along with other types of laser mediums such as neodymium, are within the solid state family of lasers. In this family, the active medium is a nonconductive solid, a crystalline material, or glass doped with a species that can emit laser light.
The typical optical cavity for concentrating light energy includes a partially transparent mirror and a totally reflective mirror with the laser medium positioned therebetween. The laser cavity may also include enhancements for concentrating the light and stimulating the emission of laser energy such as a power supply modulator for Q-switching.
Many laser systems require the power supply to provide light energy for exciting the laser medium. This process is known by those skilled in the art as optical pumping wherein the photons from the light provided by the power supply pass through the laser medium. The photons excite the species within the laser medium such that the medium generates its own light energy.
As known in the art, the efficiency of optically pumping is low by electrical standards. Typically, optically pumped commercial lasers covert 0.001 to over 30 percent of input energy into laser energy. As indicated above, the fundamental problem with optical pumping is that three energy-conversion steps are needed: one to produce the pump light, one to relay the generated light to the laser medium and one to convert the energy of the pump light into laser energy.
Although optical pumping fails to be efficient, many types of laser mediums require optical pumping. For example, far-infrared gas lasers are optically pumped because such a method provides for state-selective excitation of the laser medium. Further, solid-state lasers are optically pumped because the active species of the laser medium is locked within the matrix of an insulator which makes it impossible to excite the active species by other means such as passing an electrical discharge through the insulator matrix.
To improve the efficiency of optical pumping, many laser mediums are shaped into a rod which is pumped by a linear lamp. Typically, the rod and the linear lamp are placed in a closed-coupling configuration within a hollow reflective cavity. This configuration constitutes the pump chamber.
To further enhance optical pumping, the lamp and the rod may be positioned at the two foci of an ellipse, formed by the reflective optical cavity, so that the geometry of the reflective cavity is used to efficiently focus the pump light onto the rod. Moreover, some pumping schemes place two lamps and the rod into a dual elliptical cavity, which in cross-section looks like two overlapping ellipses, with the rod at the shared focus of the lamps.
Placing the lamp and the laser medium within a hollow cavity results in a large amount of heat being developed due to the low efficiency of optical pumping. The lamp is the major contributor of the heat since only a fraction of its energy is absorbed by the rod. Although the lamp does not require low temperatures (i.e., 25-0 degrees Celsius) for efficient operation, the rod must be cooled to this temperature range because the heat can raise the laser threshold, decrease output power, and degrade beam quality.
A typical design for cooling a laser rod, as well as the lamp, consists of flowing water through the hollow optical cavity and through a heat exchanger which removes the excess heat from within the cavity. However, since the lamp and the rod are within the same hollow optical cavity and are not separated from each other, the water used to cool the rod is needlessly heated by the lamp. This results in a significantly higher load on the cooling source than necessary for effectively cooling the rod.
Correspondingly, the present invention overcomes the above problems by providing separate cooling environments for the optical pumping medium and the laser medium.